The present invention relates to an oil and gas industry, and, more particularly to a drilling jack-up platform that can be used to develop wells in an offshore location. Even more particularly, the invention relates to a hold down system that can be used for restraining the ends of cantilevers and cantilever extensions of jack-up units.
Jack-ups, which were designed and built more than thirty years ago and even more recently, were initially designed for drilling through a slot at the stem of the unit and were not capable of working over a platform.
By the late 1970's new designs were introduced for work-over operations. These jack-ups had cantilever beams that could skid aft over the stem. The drill floor was allowed to skid port/starboard. The well drilling pattern typically covered a well center location of 40 feet aft of stern and 12 feet port-starboard of the longitudinal centerline. As the well location moved farther aft and more to port or starboard, the allowable load due to hook, rotary, setback, and later, conductor tension was significantly reduced. This limiting allowable load was reduced further as drilling equipment was upgraded adding weight.
Now, with the importance of shallow water deep reservoirs, the demand for upgrading these jack-up units for both extended reach and higher loads at the extended reach is very high. The areas, which are usually affected by the required upgrade modification, are cantilever strength due to increased bending moment and shear, hull transom and stern support reinforcement, and most importantly the hold-down clamp increase in capacity.
The hold-down clamp is a close tolerance high load structure, which keeps the forward end of the cantilever from rotating up when the cantilever is skidded aft. Often, the hold down clamp is located in the SCR room. If the hold-down clamp capacity is increased expensive modifications become necessary. Additionally, when the hold-down clamp is modified by lengthening the clamp in the aft direction, the distance between the clamp and the stern reaction is reduced, which causes higher reaction values. If the hold-down clamp is lengthened in the forward direction, the aft skidding extent is reduced. Consequently, the hold-down clamp is usually not upgraded and load chart valves are often compromised.
The present invention solves the problem of a clamp hold down by utilizing an active hold-down system.